a website called autoluminations.com or autolumination.com has these bulbs or bulbs that have those bases that would probably fit your application. the other thing you can do is open the base up and put a different connector in their to fit a bigger bulb in as well.

LEDs need some kind of way to limit the current flow. There are basically two methods- A "driver", which is a slightly complicated electronics board - example - taskled.com- A resistor - example - 2 ohms, running 3 LEDs in series from your battery.

The big challenge with auto power is voltage spikes. Very few "drivers" can handle them very well, which is why I suggested taskled drivers.

You are looking at roughly $ 100 to get that thing converted to LED, which is fine, just keep it in mind.